Automatic telephone systems



Aug. 11, 1959 A. A. cHUBB ET ALv Re- 24,679 l AUTOMATIC TELEPHONE SYSTEMS original Filed Jan. 31. 1952 5 Sheets-Sheet l ZOFUZJH/ @E LNE zo; u @2.1m

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. ATTORNEY Aug. 11, 1959 A3'A CHUBB ET AL Re. 24,679

` AUTOMATIC TELEPHONE SYSTEMS Original Filed Jan. 31,-1952 3 Sheets-Sheet 3 ZRD C 52 /N VEN Toes hem vnf-J? AL ze@ v- CTA/as www A4115:- levy 5r l- V ATTORNEY United States Patent Oiice Re. 24,679 Reiesued Aug. 11, 1959 AUTOMATIC TELEPHONE SYSTEMS Alexander Albert Chubb, Macclesfield, England, and

Maurice Moise Levy, Ottawa, Ontario, Canada, assignors to The General Electric Company Limited, London, England Original No. 2,747,019, dated May 22, 1956, Serial No. 269,158, January 31, 1952. Application for reissue October 29, 1958, Serial No. 770,888

Claims priority, application Great Britain February 2, 1951 2 Claims. (Cl. 179-18) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specilication; matter prntcd in italics indicates the additions made by reissue.

The present invention relates to automatic switching apparatus for use in automatic exchanges in which a plurality of communication channels is provided by means of a plurality of time interlaced pulse trains, and, in operation, when establishing communication between two stations connected to the exchange, apparatus associated with a first station selects a free one of the channels, a signal is transmitted to automatic switching apparatus associated with the second station identifying the selected free channel, and the said automatic switching apparatus serves to connect the second station to the identified free channel. Such automatic exchanges will be referred to hereinafter as automatic exchanges of the kind specified and examples of such exchanges are disclosed in co-pending United States patent applications Nos. 247,072, filed September 18, 1951, 257,786, filed November 23, 1951, and 257,991 and 257,992 led November 24, 1951.

The object of the present invention is to provide suitable automatic switching apparatus for use in an automatic exchange of the kind specified to connect the said second station to the channel identified by the channel identifying signal.

According to the present invention automatic switching apparatus for use in an automatic exchange of the kind specified to connect the said second station to the channel identified by the channel identifying signal, comprises two or more gate devices, one of the gate devices being for transmitting messages from the first station to the second station, and the other gate device being for transmitting messages from the second station to the first station, selector means responsive to the channel identifying signal to select gating pulses in the selected free channel, and connections for applying the gating pulses to the said gate devices whereby communication between the two stations can be established in the selected channel through the two gate devices.

One arrangement in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which Figure l is a block schematic diagram of an automatic telephone exchange of the kind specied embodying automatic switching apparatus according to the present invention.

Figure 2 is a circuit diagram of one embodiment of the invention suitable for use in the automatic exchange of Figure l, and

Figure 3 is a circuit diagram of a part shown in block form in Figure 2.

Figure 1 is a block schematic diagram of an automatic telephone exchange which is fully described in the specication of co pending United States patent application No. 257,786. This exchange will not therefore be fully described in the present specification.

The telephone exchange shown in Figure 1 is suitable for use with 2000 subscribers. Of the 2000 subscribers stations connected to the exchange, one is shown at 10 and another at 11, the station 10 being terminated in the exchange at subscribers line circuit 12 and the station il being terminated at the subscribers line circuit 13.

The exchange comprises a group of pulse communication channels the pulses in each channel having a recurrence frequency of about 8,000 P.P.S. This group of channels is provided by means including a pulse generator 14 adapted to generate pulses suitable for combination to provide the 100 channels time-interlaced at the pulse repetition frequency of 8,000 P.P.S. in each channel. The 100 channels are terminated by 100 calling units respectively of which one is shown at 15. 100 called units terminate the other ends of the channels respectively when in use, one of the called units being shown at 16. Messages between the calling and called units pass through a GO speech junction 17, a return speech junction 18 or a metering and release junction 19 as the case may be. In the event of a called subscriber being engaged a busy signal is transmitted to the calling subscriber by way of a busy junction 20.

For use in establishing calls between subscribers a number of allotters 24 and registers 23 are provided together with a signalling junction 25 and two further pulse generators 21 and 26.

Assuming the subscriber at the station 10 to be calling the subscriber at the station 11 the first operation occurs in the subscribers line circuit 12. This contains a finder which finds a free calling unit 15. An allotter 24 then cornes into operation and allots a register 23 to the calling unit 15.

By means of the allotter and a finder in the register the calling unit found by the subscribers line circuit 12 is connected to the allotted register 23. A dialling tone is then automatically transmitted to the calling subscriber.

The output of the pulse generator 21 is in the form of a recurring sequence of 20 pulses which for convenience will be divided into groups of ten each. The first ten pulses in each sequence will be referred to collectively `as the d pulses and the second ten as the u' pulses. The ten d pulses will be referred to individually as the pulses d'0 to d'9 respectively and appear at the terminals Tdo to Tdg respectively of the generator 21. The ten u pulses will be referred to individually as pulses uo to ug and appear at the terminals Tuo to Tu9 respectively of the generator 21.

Each of the calling units 15 is connected to one of the terminals Tdn to Tdg and to one of the terminals Tuo to Tu9 of the generator 21, different ones of the calling units being connected to different pairs of the terminals Td and Tu'. Thus each calling unit is identified by a different pair of -d and u pulses and, as will be described later, the pair of d and u pulses identifying the calling unit, and hence the selected channel, is transmitted to the lcalled subscribers line circuit to identify the high grade channel on which communication is to be established.

When the calling subscriber hears the dialling tone and dials the number of the cal-led subscriber, the dialling pulses are transmitted through the line circuit 12 and the seized calling unit 15 to the allotted register 23. In the register the four sets of dialling pulses are stored on four uniselectors. Four groups of ten pulses each, which will be referred to as the M, C, D and U pulses are applied to the four uniselectors in the register from the pulse generator 26. Thus the uniselectors in the register select one pulse from each of the four groups of recurring pulses applied thereto and it is arranged that these four selected pulses are combined to form a recurring output pulse which occurs in one recurring channel interval in a recurring sequence of 2,000 channel intervals. The sequence may recur for example at the rate of one per second and the 2,000 channels constitute a group of low grade signalling channels.

The recurring output pulse from the register is used as a gate pulse and permits the recurring pair of d', u pulses identified with the seized calling unit to pass to a signalling junction 25 only in the lloW grade channel interval determined by the gating pulse.

The output from the signalling junction is applied to all suhscribers line circuits. These circuits have gating pulses applied thereto however from the pulse generator 26, the gating pulses applied to each subscribers line circuit being in the channel whose number corresponds to the subscribers number on the exchange. Thus the only subscribers line circuit to respond to a pair of d', u' pulses appearing at :the output of the signalling junction is that one whose gating pulse corresponds to the nurnber dialled.

The called subscribers line circuit then hunts for a free called unit and when a free called unit is found this unit functions to select appropriate pulses from the output of the generator 14 to enable the called subscribed to establish communication in the channel terminated by the seized calling unit. The called unit forms 4the subject of the present inventio-n and one embodiment thereof will now be described in more detail with reference to Figures 2 and 3.

In Figure 2 a control terminal P12 is connected through relay contacts RBS, a relay Winding RQ and a battery BAT28 to earth. The terminal P12 is connected to one xed contact of a control bank of a uniselector forming part off the finder in the called subscribers line circuit. The wiper of this bank is normally earthed. Two terminals +12 and -12 are connected through relay contacts F2 ,and F2 respectively and capacitors C22 and C22 to a winding MW2 of ,a hybrid transformer HY2. An output winding `OW2 of the transformer HY2 has one terminal earthed and the other terminal thereof is connected through a capaci-tor C24 to the control grid of a pentode valve V24 whose cathode is earthed. The anode of the valve V24 is connected through a load resistor R62 tothe positive terminal I-IT-l-ll of a source (not shown) of D.C. Whose `.negative terminal is earthed. The anode is also connected through a capacitor C25 to an output terminal RSP2 which is connected to the return speech junction 18 of Figure l. The screen grid is connected directly to the terminal HT-.l-ll. Negative bias is applied to the control grid of the valve V24 from a bias terminal -GB21- The suppressor grid is comiected through a capacitor C26 to relay contacts CD1 and through a resistor R23 to the negative terminal GBS of a bias source (not shown).

An input terminal GSPOI which is connected to the output of the GO speech junction 17 of Figure l is connected ythrough a capacitor C27 to the control grid of a pentode valve V25 whose cathode is earthed. The control `grid of the pentode V25 is also connected through a resistor R34 to the negative terminal -GB9 of a bias source (not shown) Whose positive terminal is earthed. The anode of the pentode V25 is connected through the primary winding of a transformer XF2 to the positive terminal HT-l-ll.` of a source (not shown) of D.C. whose negative terminal is earthed. The anode is also connected through a capacitor C22 to the control grid .of a triode valve V26 whose cathode is earthed. The anode of the triode V26 is connected through a relay winding RB to the positive terminal HT4I-13 of a source (not shown) of D C. Whose negative terminal is earthed. The control grid of the triode V26 is connected through a rectifier W15 to the negative terminal GBM of a bias source Whose positive terminal is earthed. The screen grid of the pentode V25 is connected through a resistor R35 to the positive terminal HT+12. The suppressor grid is connected through a resistor R26 to the negative terminal -GBm of a bias source (not shown) Whose positive terminal is earthed, and through a capacitor C29 to the relay contacts CD1.

The transformer XF2 has two secondary windings S1XF2 and S2XF2. One terminal of the Winding S1XF2 is connected to the negative terminal -GB12 of a bias source (not shown) whose positive terminal is earthed, and the other terminal thereof is connected through a rectifier W16 to the control grid of a pentode valve V27 whose cathode is earthed. One terminal of the winding S2XF2 is connected to the negative terminal -GB12 of a bias source (not shown) whose positive terminal is earthed, and the other terminal of the winding S2XF2 is connected through a rectifier W17, and a resistor R27 to the control grid of the pentode V27.

A rectifier W12 is connected between the terminal -GB12 and the left-hand terminal of the winding S2XF2 in the drawing.

The primary winding of the transformer XF2 is tuned by a capacitor C26 which is shunted by a resistor R194.

The anode of the pentode V27 is connected through the input circuit of a low-pass filter FIL2 to the positive terminal HT|14 of a source (not shown) of D.C. whose negative terminal is earthed. The screen grid of the pentode V27 is connected through a resistor R22 to the positive terminal HTA-14 .and is decoupled by a capacitor C22. One output terminal of the low-pass filter FIL2 is connected to earth and the other output terminal is connected through the winding IW2 of the hybrid transformer HYZ to earth.

The terminal -I2 is normally connected to earth through the relay contacts F3 and a battery BAT22, and the terminal +12 is normally connected through the relay contacts F2 and through one winding of a relay F to the moving contact of relay contacts RB4. These contacts are normally open and the xed contact thereof is connected through the secondary Winding of a transformer XF2 to earth. The primary winding of the transformer XF?l is connected to terminals TR to which ringing current is applied fro-m a suitable source (not shown). The contacts F2. are bridged by a capacitor C64. One terminal of the other winding of relay F is connected through a battery BAT29 to earth and the other terminal thereof is connected through relay contacts F1 and RBI to earth. One Winding of a relay RD is connected between the right-hand plate (in the drawing) of the capacitor C22 .and earth. The other winding of the relay RD has one terminal connected to the right-hand plate of the capacitor C23 and has the other terminal connected through a battery BAT26 to earth.

A uniselector ZRU has three banks ZRUI, ZRUZ and ZRU3, each of which has a home contact and bank contacts. The bank ZRUl has ten banks contacts which are connected to the translator 25 to be described later. The wiper of the bank ZRU1 is connected through `a resistor R29 to the control grid of a gas-lled triode valve V28. The cathode of the valve V22 is connected to the negative terminal of a bias source GBM whose positive terminal is earthed. The anode of the valve V22 is connected through relay contacts DA1 to one terminal of a relay winding DA. The other terminal of the winding DA is connected through relay contacts RQ1 and RBZ in parallel to the positive terminal HT-l-IS of a source (not shown) of D.C. `Whose negative terminal is `earthed.

The bank ZRUZ is a homing bank and has its homing arc BC6 connected to earth through relay contacts DAZ. The wiper of the bank ZRUZ is connected through contacts ZRUdm, operating winding-ZRU, a relay winding CD and a battery BAT31 in series to earth. The home contact of the bank ZRU2 is connected through relay contacts RQ2 to earth.

1 The bank ZRUS has ten bank contacts which are connected to ten terminals Tu0 to Tu3 respectively. The wiper of the bank ZRU3 is connected through a resistor R to the xed contact of contacts CD1.

A uniselector ZRD has three banks ZRDI, ZRDZ and ZRD3, each of which has a home contact =bank contacts. The bank ZRDI has ten bank contacts Which are connected to the translator 25. The Wiper of ZRDI is connected through a resistor R11 to the control grid of a gas-filled triode V23 whose cathode is connected to earth through a bias source GB15. The anode of the valve V20 is connected through relay 4contacts UA1 to one terminal of a relay winding UA and the other terminal of the winding UA is connected through the relay contacts RQl and RBZ to the terminal HT-|15.

The bank ZRDZ is a homing bank and the homing arc BC, is connected through relay contacts UA2 to earth, and the home contact through RQZ to earth. The wiper of the bank ZRDZ is connected through the mechanically operated contact ZFDdm, the operating winding ZRD, the relay Winding CD and the battery BAT31 in series to earth.

The bank ZRDS has ten bankcontacts which are connected to ten terminals Td0 to Tdg respectively. The wiper of the bank ZRD3 is connected through a rectifier W20 to the fixed contact of contacts CD1.

The moving contact of the contact CD1 in addition to being connected through the capacitors C25 and C20 to the suppressor grids of the pentodes V2.1 and V25 respectively is connected through a resistor R12 to earth and directly to the moving contact of contacts RD1. The fixed contact of contacts RDl is connected through a resistor R43 to earth and through a capacitor C33 to the control grid of a triode valve V31 whose cathode is earthed. Negative bias is applied through a resistor R41 to the control grid of the triode V31 from the negative terminal G1310 of a bias source (not shown) whose positive terminal is earthed. The anode of the valve V31 is connected through a `capacitor C31l to an output terminal ASP1, and through .a resistor R15 to the positive terminal HT+16 of a source (not shown) of D.C. whose negative terminal is earthed. The terminal ASP1 is connected to the metering and release junction of Figure l.

The translator 25 is connected through relay contacts RQ3 to the positive terminal HT|17 of `a source (not shown) of DC. whose negative terminal is earthed. Ten terminals Tu0 to Tu0 and ten terminals Td'0 to Td0 are connected to the translator, and a further terminal CS2 is connected to the called subscribers line circuit to receive the pairs of d' u' pulses passed by the called subscribers line circuit.

Referring now to Figure 3, this is a theoretical circuit ldiagram of the translator 25. The translator comprises two groups of gas-lilled triode valves each group containing ten valves. A rst of the groups contains ten triodes V32 to V41 whose cathodes are connected to earth through resistors. R15 and R55 respectively, and directly to the ten blank contacts respectively of the uniselector bank ZRU1. The anodes to the triodes V32 to `V11 are connected together and through the relay contacts to RQ3 to the terminal HT-1-17. The terminals Tu0 to Tu0 are connected through ten rectiiers W21 to-W30 ten resistors R05 to R75 and ten rectiliers W100 to W103 respectively in series to the control grids of the triodes V32 to V11. The terminal CS2 is connected ythrough ten resistors R30 to R05 to the junctions of the rectiers and resistors connecting the terminals Tu0 -to Tu0 respectively to the control grids of the triodes V32 to V41. The control grids of the triodes V32 to V11 are connected through capacitors C103 to C112 and resistors 'R201 to R215 respectively to earth.

'V'Dhe' second group contains ten triodes V12 to V51 whose cathodes are earthed through resistors R50 to R05 respectively. The cathodes of these valves are also connected directly to the ten bank contacts respectively of the uniselector bank ZRDI. The anodes of the valves V12 to V51 are connected together andthrough the relay contacts RQ3 to the terminal HT--i-17. The terminals Td0 to Td9 are connected through ten rectiers W31 to W10 ten resistors R70 to R05 and ten rectiers W110 to W110 respectively in series to the control grids of the valves V42 to V51. The terminal CS2 is connected through ten resistors R35 to R105 to the junctions of the rectiers W31 to W10 and resistors R05 to R35 respectively.

ln operation the d and u pulses arriving at the terminal CS2 from the called sub-scribers line circuit are applied to the control lgrids of the valves V32 to V51 through the resistors R to R105 and pulse lengthening circuits comprising the rectiers W to W113 and capacitors C103 to C122. The rectiiiers W21 to W10 are, however, conducting to these pulses except the rectiers to which d' and u pulses are applied from the terminals Tu0 to Td3 simultaneously with the d and u pulses arriving at the terminal CS2. In this example it Iwill be assumed that the pulses d'0 and u1 appear at the terminal CS2 simultaneously with the pulses d'0 and u1 applied at the terminals Td0 and Tu1. Thus the rectiers W31 and W22 are non-conducting in this example and permit the d'0 .and u1 pulses applied to the terminal CS2 to pass to the control grids of the valves V12 and V33 respectively. These tw'o valves strike and hence their cathodes become positive.

When the wiper of the :bank ZRU1 reaches the bank contact connected to the cathode of the valve V33 the positive potential appears at the lcontrol grid of the valve V25 (Figure 2) and this valve strikes. Similarly the valve V20 (Figure 2) strikes when the wiper of the bank ZRDI reaches the bank contact connected to the cathode of the valve V42.

Referring to Figure 2, when the valves V23 and V20 strike the relays DA .and UA become energised by the anode circuits of these two valves. Tlrus the contacts DA1, DAZ, UA1 and UAZ are operated. The contacts DA1 and hold the relay DA and extinguish the valve V20 and the contacts DA2 break the automatic stepping circuit of the uniselector ZRU. The contacts UA1 hold the relay UA and extinguish the valve V23, and the contacts UAZ break the automatic stepping circuit of the uniselector ZRD.

Thus the wipers of the -banks ZRD3 and ZRU3 are arrested on the bank contacts connected to the terminals 'I`d0 and Tu1 respectively. The pulses d0 and u1 are applied to these terminals respectively from the high frequency pulse generator. In the absence of a d0 pulse the rectifier W20 is conducting and hence the u1 pulses are dropped across the resistor R40. The occurrence of a d0 pulse renders the rectifier W20 non-conducting and hence the u1 pulse occurring during each d0 pulse passes to the contacts CD1 that is to say pulses in channel No. l. These contacts close simultaneously with the opening of the automatic stepping circuit of the selectors and the pulses in channel No. l pass to the suppressor grids of the valves V21 and V25.

Thus lunmodulated pulses of anode current flow in the valves V2.1 and V25 which are arranged to be normally non-conducting by the bias applied thereto from the terminals -GB3 and -GB10 respectively. The pulses passed Iby the valve V25 are applied through the capacitor C20 to the control grid of the valve V20. Thus, pulses of anode curent flow in this valve which is arranged to `be normally non-conducting by the bias applied thereto from the terminal GB11. Thus the relay RB becomes energised and the contacts RBI and RB4 thereof are operated.

The contacts RBS put an earth on the terminal P12. The contacts RB2 close and hold the relays DA and 7 UA when the? relay RQ lbecomes -de-energsed on the operation of the contacts RBS.

The contaets--RB4 close and apply ringing `voltage from the transformer XF3 to the called subscribers station via V'the terminals +l2fand -I2. When the called subscriber answers the relay F `becomes energised, the energising circuit being from earthl through thev battery BAT33 the contacts F3, the called suhscribers line, the contacts F2, the'rel'ay winding F, the contacts RB4 and the secondary winding of the transformerXF3 back to earth. The contacts RBI and F1 hold the relay F.

The relay RD then becomes energised, the energising circuit being from -earth through the battery BAT 3D, one winding of the relay RD, the contacts F3, the called subscribers line the contacts F2 andthe other winding of the relayRD back to earth.

The contacts RD1 then apply the pulses in channel No. l through the valve V31 to the terminal ASP1 and `thence through the metering and release junction (19, Fig. l) to the calling unit 15.

All pulses from the terminal GSPO1 are passed to the control grid of the pentode V25 which is gated by channel No. l pulses as previously described. Thus only the pulses in channel No. l pass to the transformer XF2.

The primary winding is tuned by the capacitor C31, to a periodicity of approximately twice the width of the pulses applied thereto from the valve V25, and is heavily damped by the resistor R131. The winding S2XF2 has more turns than the winding S2XF1 and hence provides a greater output voltage'than S2XF1.

The terminal --GB13 is arranged to be about ve volts less negative than the terminal -GB12.

Assuming Ithe charge in the capacitor C31 to be such that the potential of the upper plate thereof in the drawing is between that of -GB13 'and -GB12, the rectiliers W15 to W11, are non-conducting. When a pulse arrives at the primary winding of the transformer XF2 from the valve V the leading edge of the pulse shock excites the transformer. The first, and negative, half-cycle of the free oscillation is applied to the anode of W15 which, therefore, remains non-conducting, and to the cathode of W11 which becomes conducting and hence C31 discharges through R37 and W17 until the potential of its upper plate in the drawing equals the potential of the terminal -GB12. Any `funther negative excursion at the cathode of W11 is damped by W13. Simultaneously W19 becomes conducting and as a result the capacitor C111 discharges further and its upper plate is left at a potential somewhat below that of the terminal G1312 Just as this negative half-cycle ends, the lagging edge of the pulse arrives and again the transformer XF2 is shock-excited but -this time in the opposite sense. The tirst, and positive, half-cycle of thissecond free oscillation has no effect on W17 and W13. The capacitor C31 is charged, however, through W16 to a value dependent upon the amplitude ofthe pu-lse applied to the transformer XF2, and lying between the potentials of the terminals -GB12 and -GB13.

The damping provided by the resistor R13.,l is arranged to be sullicient to prevent subsequent half-cycles from affecting the charge in the capacitor C31.

Thus the capacitor C31 presents relatively broad pulses to the valve V21 in response rto relatively narrow pulses passed by the valve V23, the amplitude of the broad pulses being dependent upon the amplitude of the narrow pulses.

The broad amplitude-modulated pulses are demodulated by being pressed through the low-pass iilter FIL2 and the speech voltages are passed through the transformer HY2' the capacitors C22 and C23, the contacts F2 and F3, and the called subscribers line circuit to the called subscribers line.

Speech voltages from the called subscriber are passed through his line circuit, andthe hybrid transformer HY2 to the control grid of'the pentode valve V21. Here ythey serve to amplitude-modulate the pulses (in channel No. l) applied'from'the anode of V2.1 to` the terminal -RSP2. These pulses `vare applied through the Return speech gu-nction to the calling unit.

When a call is ended and the calling subscriber replaces his handset onits rest it is arranged thatthe calling unit is released and hence pulses arriving at the terminal GSPO1of Figure 2 cease and the relay RB becomes deenergised. The contacts RBI reopen and release the relay F. The `contacts RB?. open and release the relays DA and UA. Thusthe contacts DAZ and UAZ close and the uniselectors ZRU and ZRD home. The called unit is then ready for use in mak-ing another call.

Although an arrangement has been described in which two pulses (d, u) are transmitted to the called unit in other systems `a. different number of pulses may betransmitted. For example where more than channels are provided it will be necessary to transmit three pulses, one of which is representative of the 100s the: second of the lDs and the third ofl the units in the selected channel number. A further group of ten tubes is then added in Figure 3 and appropriate gating pu-lses applied thereto. Likewise a further uniselector is added in Figure 2 and controlled by the tubes in the third group in Figure 3.

'We claim:

El. In combination, a selector device having a plurality of input terminals, an output terminal and selector means for selectively connecting the input terminals to said output terminal, means to apply pulse trains of different phases to said input terminals respectively, a control circuit to actuate said selector means, a source of control voltage connected Ato said control circuit to cause said selector means to Vselect one of said input terminals for connection to saidoutput terminal, a pulse demodulator, a pulse modulator and means to connect said output terminal to said demodulator and modulator] i12. ln combination, a selector device having a plurality of input terminals, an output terminal and selector means for selectively connecting the input terminals to said output terminal, means to apply pulse trains having different channel identifying signals to `said input terminals respectively, a control circuit to actuate said selector means, a source of control voltage connected to said control circuit to cause sai-d selector means to select one of said input terminals for connection to said output terminal, a pulse demodulator, a pulse modulator and means to connect said output terminal to said demodulator and modulator.]

, [3. A combination as set forth in claim 2 wherein each channel identifying signal includes a pulse whose instant of occurrence identities a different pulse train, and wherein the selector means comprises a group of gas iilled electron discharge tubes each of which has an anode, a cathode and a control electrode, a plurality of gate devices in the control electrode circuits of the several discharge tubes respectively, means for causing said gate devices to open in turn, and circuit means for applying a selected one of said channell identifying signals to the control electrodes of all said discharge tubes through said gate devices whereby the pulse of said selected channel identifying signal passes to the control electrode of only one of said discharge tubes to strike said tube and identify a selected pulse train] E4. In combination, a selector device having a plurality of input terminals, an output terminal and selector means for selectively connecting the input terminals to said output terminal, means to apply pulse trains of different phases tol said input terminals respectively, a control circuit to actuate said selector means, a source of control signals connected to said control circuit to cause said selector means to select one of said input terminals for connection to said output terminal, a pulse demodulator,

a pulse modulator, and means to connect said output terminal to said ydemodulator and modulaton] [5. A combination as set forth in claim 4, wherein each control signal includes a pulse, the instants of occurrence of pulses in different ones of said control signals identifying different ones of said pulse trains, and wherein the selector means comprises 'a group of gas-filled electron discharge tubes each having an anode, a cathode, and a control electrode, a plurality of gate devices in the control electrode circuits of the discharge tubes respectively, means for causing said gate devices to open in turn, and circuit meansI for applying a selected one of said control signals to all said gate devices whereby the pulse of the selected control signal passes to the control electrode of only one of said discharge tubes to strike said tube and identify one of 'the said pulse trains to be selected] 6. In combination, a selector device having a plurality of input terminals, an output terminal and selector means for selectively connecting the input terminals to said output terminal, means to apply pulse trains having different channel identifying signals to said input terminals respectively, a control circuit to actuate said selector means, a source of control voltage connected to said control circuit to cause said selector means to select one of said input terminals for connection to said output terminal, a pulse demodulator, a pulse modulator and means to connect said output terminal to said demodulator and modulator, each channel identifying signal including a pulse whose instant of occurrence identifies a different pulse train, the selector means comprising a group of gas filled electron discharge tubes each of which has an anode, a cathode and a control electrode, a plurality of gate devices in the control electrode circuits of the several discharge tubes respectively, means for causing said gate devices to open in turn, and circuit means for applying a selected one of said channel identifying signals to the control electrodes o i all said discharge tubes through said gate devices whereby the pulse of the said selected channel identifying signal passes to the control electrode of only one of said discharge tubes to strike said tube and identify a selected pulse train.

7. In combination, a selector device having a plurality of input terminals, an output terminal and selector means for selectively connecting the input terminals to said output terminal, means to apply pulse trains of dierent phases to said input terminals respectively, a control circuit to actuate said selector means, a source of control signals connected to said control circuit to cause said selector means to select one of said input terminals for connection to said output terminal, a pulse demodulator, a pulse modulator, and means to connect said output terminal to said demodulator and modulator, each control signal including a pulse, the instants of occurrence of pulses in diyjerent ones of said control signals identifying dijerent ones of said pulse trains, the selector means comprising a group of gas filled electron discharge tubes each having an anode, a cathode, and a control electrode, a plurality of gate devices in the control electrode circuits of the discharge tubes respectively, means for causing said gate devices to open in turn, and circuit means for applying a selected one of said control signals to all said gate devices whereby the pulse of the selected control signal passes to the control electrode of only one of said discharge tubes to strike said tube and identify one of the said pulse trains to be selected.

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